"The objective of having an inexpensive material that can be stored easily until needed, applied easily, and provide frost protection has existed since the mid 1950's. Many materials have been examined. These fall into several categories but generally, they have been materials that allegedly either changed the freezing point of the plant tissue; reduced the ice-nucleating bacteria on the crop, thereby inhibiting ice and frost formation; or affected growth, i.e. delayed dehardening or work by some `unknown mode of action`. To our knowledge, no commercially available material has successfully withstood the scrutiny of a scientific test." (K. B. Perry, 1998, Basics of Frost and Freeze protection for horticultural crops). HortTechnology 8(1):10-15. See also Warmund et al, Advances in Strawberry Research 1994, pages 20-25, who also found no significant effect of a frost protectant chemical. As stated by Perry (1998) there are four areas of chemical development related to frost protection: 1) materials that change the freezing point of the plant tissue or water; 2) reduce the populations of ice nucleating bacteria on the crop surface, thereby inhibiting ice formation on the crop surface; 3) delay dehardening; 4) genetic engineering to increase cold hardiness.
Patents related to the first area of technology include: Barr et al U.S. Pat. No. 5,133,891, which relates to treatment of plants for frost protection by the application of an organic chemical; Shin et al U.S. Pat. No. 5,276,006, which relates to a cryoprotectant composition that increases the tissue resistance to freeze damage; Savignano et al U.S. Pat. No. 5,653,054 which relates to a process for preventing frost formation on plants that involves lowering the freezing point of water; Lengyel U.S. Pat. No. 4,597,883 which relates to a composition and method for minimizing frost damage to plants that includes a salt-based solution to lower the freezing point of water and resist cell damage to freezing temperature; Artozon U.S. Pat. No. 5,618,330 which relates to plant treatment compositions and processes that involve high concentrations of salts to protect against frost damage; and Suslow et al U.S. Pat. No. 5,633,450 which relates to chitinase-producing plants that are resistant to cold damage.
Patents related to the second area of technology include: Lindow U.S. Pat. No. 4,432,160 which relates to the microbial inhibition of frost damage to plants which is a method involving the selection and use of ice nucleating deficient bacteria to prevent freezing damage; and Orser et al. U.S. Pat. No. 4,766,077 which relates to ice nucleation deficient microorganisms made by genetic manipulation which involves a method to produce ice nucleating deficient organisms for application to plants as a frost protectant.
The third area of technology does not directly prevent frost damage, but instead delays the development of frost-sensitive reproductive tissues in the early growing season so that frost does not occur when frost-sensitive tissues are exposed. There are also non-chemical approaches to frost protection that include Muscatell U.S. Pat. No. 4,434,345 which relates to a microwave system for frost protection of fruit trees that generates heat to prevent freezing, and Donohue et al U.S. Pat. No. 4,901,472, which relates to a method and apparatus for the protection of citrus trees from frost damage using an insulating pad for the trunk of the tree. M. Wisniewski and M. Fuller (Ice nucleation and deep supercooling: new insights using infrared thermography in: Cold Adapted Organisms: Fundamentals and Applications. Eds. R. Margesin and F. Schinner, Landes BioScience, Austin, Tex.) indicate that the application of a silicone grease to plant surfaces makes a water repellant film that prevents ice from propagating into the plant and allows the plant to supercool, thus preventing frost damage. However, the application of silicon grease to plants is phytotoxic since it prevents the exchange of gases to and from the leaf. Therefore, there is still a need for a cost effective, nontoxic agent to prevent freezing damage that does not interfere with the exchange of gases, or other physiological processes of plants, and particularly horticultural crops.
The fourth area of technology relates to genetic engineering of plants to increase their tolerance to cold. Caceci et al U.S. Pat. No. 5,932,697 and U.S. Pat. No. 5,925,540 relate to methods of synthesizing a peptide that increases cold hardiness. Guy et al U.S. Pat. No. 5,837,545 relates to a method of synthesizing polypeptides to increase cold hardiness.